The present invention relates to a method and apparatus for electrode dressing of an Electro Discharge Machining (EDM) suitable for creating holes in components.
In one known example, electro discharge machining is used to form cooling holes in turbine blades of a gas turbine engine. One cause of defects and non-conformance for holes in blades is wear on the electrode. To avoid wear, the electrode is redressed prior to cutting each hole. The redressing operation is carried out, typically, on a copper template. The “squarer” the end of the electrode after redressing, the cleaner the subsequent hole cut in the turbine blade. In order to ensure that the electrode is redressed properly, the template used for redressing should comprise a smooth, un-pitted surface. In the known process, the operator manually unclamps, adjusts the position of the copper template and reclamps, for each operation, so that the electrode contacts an un-pitted area.
This re-adjustment operation is awkward and time consuming due to this clamping method (see FIG. 1) and as a result, is not always carried out by the operator, hence cooling holes are not always formed properly. This can lead to inadequate cooling fluid flow and unwanted thermal gradients throughout the component, reducing its service life. Furthermore, the manual adjustment is imprecise and the template is often underused or the electrode is presented to a pitted region where poor redressing also results in a substandard hole being formed in the component.